Chemical treatment of metal

ABSTRACT

A method for preparing metal surfaces for receipt of a coating such as a paint or adhesive (whereby increased coating adhesion and corrosion resistance is achieved) and the treated metal per se, are disclosed. The method comprises contacting the metal surface with various phosphinyl derivatives.

United States Patent Inventor Francis Clyde Ranch Stamford, Conn.

Appl. No. 855,399

Filed Sept. 4, 1969 Patented Oct. 26, 1971 Assignee American CyanamidCompany Stamford, Conn.

CHEMICAL TREATMENT OF METAL 10 Claims, No Drawings Int. Cl C231 7/08Field of Search l48/6.l5,

[56] References Cited UNITED STATES PATENTS 2,268,158 12/1941 Marvel260/946 Primary Examiner-Ralph S. Kendall Attorney-Frank M. Van RietCHEMICAL TREATMENT OF METAL BACKGROUND OF THE INVENTION The use ofvarious chemical materials in the treatment of metal surfaces to therebyrender them corrosion resistant is well known to those skilled in theart. For example, U.S. Pat. No. 1,798,218 describes a method wherebycertain molybdenum compounds are utilized, whereas US. Pat. NO. 1,911,537 discloses the use of dicarboxylic and hydroxy-dicarboxylic acidsfor the same purpose. Phosphoric acid salts, US Pat. Nos, 1,936,533;1,936,534; 2,952,669 phosphates, (U.S. Pat. Nos. 2,224,695; 2,472,099;2,769,737 and orthophosphoric acid-chlorinated hydrocarbon solutions,(US. Pat. No. 2,789,070) have also been disclosed for similar purposes.

While these prior art techniques generally provide acceptable corrosionresistance, they usually fail in regard to the ad hesion of surfacecoatings such as paints, varnishes, enamels, adhesives etc. thereto.Additionally, many of these antiquated systems are severely polluted bywater, i.e., when contacted with water they tend to peel, blister etc.

SUMMARY 1 have found that the adhesion of coatings to metals can bematerially increased or strengthened by first treating the metal with achemical material which is chemisorbed, i.e., chemically reacted with orabsorbed via strong bonds. In this manner, a foundation or integralchemical or chemically bound coating is formed on the metal surface viareaction with the metal, which foundation is then more susceptible to anultimate or surface coating such as a paint or adhesive, than materialsutilized in the past. My method results in coatings which are moresecurely bonded or adhered to the foundation layer because he foundationis chemically bonded to the metal and, in a preferred embodiment, anultimate coating is chemically bonded to the foundation. That is to say,upon treating the metal according to my novel method, a reaction, asmentioned above, causes a strong bonding of the phosphinyl derivativelayer to the metal. There then remains, in my preferred embodiment, asecond reactive group in the phosphinyl derivative layer, which group isfree to react with an exterior surface coating. This free reactive groupchemically combines with the surface coating applied thereto to producea metal having a coating tightly bonded thereto. Additionally, thecorrosion resistance of the metal treated according to the presentinvention, with or without an extraneous coating on its surface, is atleast as effective and in many cases, better than known corrosionresistant systems.

DESCRlPTlON OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS My novelprocess comprises treating a metal surface, such as that of aluminum,steel, iron, copper, titanium, etc. with a reactive phosphinylderivative. The useful phosphinyl derivatives have the formula wherein Rand R are, individually, a phenyl group, an alkyl group of one-fourcarbon atoms, inclusive, an allcoxy group of one-four carbon atoms,inclusive, a benzyl group, a vinyl group, a substituted phenyl group, asubstituted alkyl group of one-four carbon atoms, inclusive, asubstituted alkoxy group of one -four carbon atoms, inclusive, or asubstituted benzyl group, said substituents comprising NH OH, SH or apolymerizable a, l3-ethylenically unsaturated aliphatic group and Re isNH-,, OH, SH or any group represented by R, above.

While not wishing to be bound by any particular theory, I believe thatthe C= and P=O groups of the phosphinyl derivatives react with the oxidelayer formed on the surface of the metal to be treated. The existence ofsuch oxide layers is well recognized by cogent workers in the art. Suchlayers form upon exposure of the metal to the atmosphere. After thephosphinyl derivative-oxide bonding is complete, the reactive groups ofthe phosphinyl foundation layer, if any, are then free to react with thesurface coating, i.e., paint, adhesive etc., thereby chemically bondingthe coating to the metal. The phosphinyl derivative-oxide bonding ispseudochemical in nature and can be more accurately described as achemisorption or chelation of the derivative by the metal.

The phosphinyl derivative foundation layer may be applied to the metalsurface, the metal'first being thoroughly cleaned such as by degreasingwith trichlorethylene etc., or other common techniques, by immersing,dipping, painting, brushing, wiping, spraying etc. the metal article tobe treated with solutions of one or more of said phosphinyl derivatives,for a length of time such that the metal surface absorbs or reacts witha sufficient amount of the derivative. The metal is then merely removedfrom the solution and allowed to dry.

Additionally, the phosphinyl derivative can be applied to the metal byfirst incorporating it into the surface coating material, e.g., thepaint or adhesive, and then applying the surface coating. In thismanner, the phosphinyl derivative can be added, for example, to thepaint vehicle, and the paint then can be sprayed etc. onto the metal.Similarly, the phosphinyl derivative can be added to one part of atwo-part adhesive system and the adhesive can then be applied to themetal, In each instance, the reactive groups of the surface coatingmaterial will react with the appropriate groups of the phosphinylderivative, if present, while the derivative itself reacts with theoxide on the metal surface, as more specifically r described above.

The solution of phosphinyl derivative can comprise from about one partto about 50 parts of the derivative per 1,000 parts of solvent, e.g.,ethanol, methanol, water etc. The treatment is preferably conducted atroom temperature although higher or lower temperatures may be utilized,if desired. Complete chemisorption of the phosphinyl derivative onto themetal surface is generally achieved in from about 10 to about 20minutes, the lower the derivative concentration, the longer the reactiontime necessary.

As mentioned above, when a group reactive with the surface coating orlayer is present on the phosphinyl derivative, the foundation layer ofderivative affords a chemically available site whereby the reactivegroups of a paint or adhesive layer may chemically react to thereby forma tightly adhering coating or layer. Examples of paints, adhesives orother coating or layer. Examples of paints, adhesives or other coatingswhich may be used include epoxy paints and adhesives. i.e. thosecontaining chemically available groups; urethane paints and adhesives,i.e., those containing chemically available NCO groups; acrylic paintsand adhesives, i.e. those containing chemically available groups; vinylpaints and adhesives, i.e., those containing chemically available-Ch=Ch-groups and the like. As is clear from the enumeration of thechemically available groups of the above-mentioned coatings, theavailable group may be free to react with the available group of thephosphinyl derivative layer previously applied to the metal surface.These reactive groups are explicitly represented, as discussed above, byNH Ol-l, SH and unsaturated aliphatic groups and in the case of epoxyand urethane paints and adhesives would be NH OH Or SH substitutedgroups, while in the case of acrylic or vinyl paints and adhesives, thereactive group of the phosphinyl derivative would be the unsaturatedsubstituent, including vinyl, allyl etc.

The coating, e.g., a paint, can be applied in a condition such that thereaction concurs while the paint vehicle evaporates or in a conditionthat the paint must more completely polymerize or cure before it forms auseful coating. In the latter case, if the functional group of thephosphinyl derivative is such that it initiates polymerization of thepaint, the paint may be applied in a prepolymer or semipolymercondition. An example of such a treatment is illustrated by the use ofan hydroxy group containing derivative and an epoxy prepolymer. In thiscase, the hydroxy group both reacts with and cures (polymerizes) theepoxy prepolymer.

Additionally, I have found that my novel processing procedure can beutilized in conjunction with known procedures to obtain apseudosynergistic effect. For example,

I can improve the corrosion resistance of metals treated according to myinvention by first treating the metal with an inorganic chromate in amanner known in the art. Furthermore,

the chromate (e.g., potassium dichromate; chromic acid solution, etc.)may be incorporated into the solution of phosphinyl derivative of mynovel method before treating the metal according to my invention. Inthis manner, the corrosion re sistance of the metal is further increasedwithout loss of the enhanced surface coating adherence mentioned above.

The phosphinyl derivatives utilized in the present invention are wellknown to those skilled in the art as are methods for their production.Generally, they may be produced by the age on the X-axis and the currentcrossed Claisen Condensation Reaction, see Morrison et al., 3

claims. All parts and percentages are by weight unless other- Indetermining the corrosion rate according to table I, a modifiedpolarographic apparatus is used. The apparatus includes an appropriateexperimental cell, a potentiostat and recorder. A three electrode systemis used: (l) an aluminum electrode; (2) a calomel reference electrodeand (3) a platinum counter electrode. The aluminum electrode is 0.030inch diameter wire which is potted with a commercially available epoxyresin which is then sanded off so that the actual electrode area is thelongitudinal cross section of the wire. For the control, the samples aremerely untreated electrodes. For examples 1-6, the freshly polishedaluminum electrode is dipped in a solution of the phosphinyl derivativefor about 10 minutes.

After treatment, the aluminum electrode is placed in the cell and theappropriate electrical connections to the potentiostat made. Theelectrolyte is a citrate buffer of pH 4.6. The initial potential of thealuminum electrode is then set at --l.0 volts, with respect to thereference electrode. The voltage scan is then turned on. A sweep rate of0.2 volts/minute in the positive direction is used and the currentdeveloped is measured on the recorder. The resulting polarization curve,volton the Y-axis, may then be analyzed to give the corrosion rate.

The method of analysis is that used by Evans et al., J. Electrochem.Soc. l08,509(l96l). v,l

TABLE I Corrosion rate Breakdown (mg/din; potential Example Phosphmylderivative Solvent day) (volts) Control No treatment 6.43 59 11-d1methylphosphinyl)-2-propanone- 0.92 78 21-(diphenylphosphinyl)-2-propanone 1.05 +.8l 3 1(dibenzylphosphinyl)-3phenyl-2-propnnone.- 1.56 73 4.. l-(benzylrnethylphosphinyD-2propanone.0.75 77 5 -(dimethylphosphinyl)-2-butunone 1.38 +.82 62-(dimethoxyphosphinybacetamlde- 1.50 +.92

Organic. Chemistry, Allyn & Bacon, Inc., Boston, l959, page 703. Atypical reaction would proceed according to the equation:

R being as represented by R, R or R above. An additional method consistsin using a halide according to the equation:

tion only and are not meant to be construed as limitations on thepresent invention except as set forth in the appended EXAMPLE 7 Aluminumpanels, 3X5inches, are degreased by dipping in benzene and furthercleaned by dipping in a hot 10 percent solution of a commerciallyavailable aluminum cleaner. The panels are then allowed to dry in air.One panel is then immersed in a solution ofZ-(dimethoxyphosphinyl)acetamide in water. After 15 minutes the panel isremoved and allowed to dry.

The panel is then spray painted with a commercially available epoxypaint and allowed to dry and cure for 5 days at room temperature.

The painted panel is then subjected to a modified version of theCross-Hatch Tape Test formulated by the National Coil CoatersAssociation In the test, the painted surface is cut 10 times verticallyand 10 times horizontally with a razor blade, the scratch lines beingapproximately 5 mm. apart. Scotch cellophane tape No. 600 is appliedover the test area and rubbed with sufficient pressure to remove all airbubbles. The panel is allowed to set for 10 minutes and the tape is thenremoved sharply with a pull at right angles to the test surface. Avisual examination allows a reasonably accurate estimation of thepercent finish remaining on the panel in the test area.

The average results of test conducted on panels treated according toexample 7, in addition to the results recorded utilizing differentphosphinyl derivatives according to the process of the present inventioareset forth in table ll. v,2

TABLE II Average percent of Number of finish repanels Example Phosphinylderivative Solvent maining tested 7 2-(dimethoxyphosphlnyl)acetamideWater 95 6 8 2[l:1S(g-hydr0xyphenyl)ph0sphinyl]-4'-hydroxym do 82 6 openone. 9 l-(pamlnophenyl)-3-lbis(p-aminobenzyD-phosphinylldo 84 62-propan0ne. l lpis(p-mercaptophenyl)phosphinylIacetaldehyde ..d0 79 611. lbis(hydroxyrnethyl)phosphlnyl]acetie acid ..do.. 83 6 l2 Control(no treatment) 20 30 EXAMPLE l3 Utilizing the procedure of example 1except that l- [(aminomethoxy)rnethylphosphinyl1-2-propanone isemployed, a corrosion resistant panel is produced.

EXAMPLE 14 The procedure of example 7 is followed except that 2-[bis(p-vinylphenyl)phosphinyllacetamide is utilized as the foundationlayer and the surface coating is a commercially available white acrylicpaint. A panel similar in surface coating retention to that of saidexample is obtained.

EXAMPLE l5 The procedure of example 7 is again followed except thatafter cleaning the surface of the metal panel with a degreasing agentand an alkali cleaning agent, 3 parts ofl-[bis-(p-hydroxylbenzyl)phosphinyl12-hexanone are added to 100 parts ofthe catalyst-curing agent package of a commercially available, 2-package polyurethane adhesive composition. After blending the contentsof the two packages together, the resultant mixture is applied to theclean a'llfiinum panel and cured under the recommended conditions. Theadhesive is bonded more tightly to the metal panel than it is on acontrol specimen formed without the added hexanone.

EXAMPLE l6 The procedure of example 7 is again followed except that inplace of the epoxy paint used therein, a commercially available epoxyadhesive is used. The bonding of the adhesive to the metal is similar tothat of the paint of said example.

EXAMPLE 17 The procedure of example l t is again followed except that acommercially available vinyl paint is used in place of that paint ofsaid example and the metal used is steel. The adhesion of the paint. tothe steel panel is superior to that of a panel coated without thefoundation layer of propanedione.

EXAMPLE 18 The procedure of example 1 is again followed except that themetal treated is stainless steel. Similar results are recorded.

EXAMPLE 19 Following the procedure of example 1 except that the metaltreated is carbon steel, effective corrosion resistance is observed.

EXAMPLE 20 The procedure of example 7 is followed with replacement ofthe aluminum panels with similar shaped sections of titanium sheet. Theadherence of the epoxy paint to the phosphinyl derivative foundationlayer is 35 percent (control-no treatment-O percent).

EXAMPLE 21 The use of nickel sheet for the aluminum panel of example 3results in a good corrosion resistant panel.

EXAMPLE 22 The process of example 10 is followed except that acommercially available, corrosion resistant nickel-chromium alloy isused in place of the aluminum panels thereof. The average percent offinish remaining after applying the tape test is 74 percent, 6 panelstested.

lclaim:

l. A method which comprises coating a metal surface with a compoundhaving the formula R i p H ll 0 5 NH:, OH, SH or any group representedby R, above.

2. An article of manufacture comprising a metal surface having coatedthereon a compound having the formula set forth in claim 1.

3. A method according to claim 1 wherein the meant surface is coatedwith said compound and a surface coating having groups chemicallyreactive with at least one of the groups of said compound is coatedthereon.

4. A method according to claim 1, wherein said compound is coated ontosaid metal surface as a mixture with a surface coating having groupschemically reactive with at least one of the groups of said compound.

5. A method according to claim 1, wherein said compound is dimethylZ-phosphonoacetamide.

6. A method according to claim I wherein said metal is aluminum.

7. A method according to claim 3 wherein said surface coating is apaint.

8. A method according to claim 4, wherein said surface coating is apaint.

9. A method according to claim 3 wherein said surface coating is anadhesive.

10. An article according to claim 2 wherein said metal is aluminum.

2. An article of manufacture comprising a metal surface having coatedthereon a compound having the formula set forth in claim
 3. A methodaccording to claim 1 wherein the metal surface is coated with saidcompound and a surface coating having groups chemically reactive with atleast one of the groups of said compound is coated thereon.
 4. A methodaccording to claim 1 wherein said compound is coated onto said metalsurface as a mixture with a surface coating having groups chemicallyreactive with at least one of the groups of said compound.
 5. A methodaccording to claim 1, wherein said compound is dimethyl2-phosphonoacetamide.
 6. A method according to claim 1 wherein saidmetal is aluminum.
 7. A method according to claim 3 wherein said surfacecoating is a paint.
 8. A method according to claim 4, wherein saidsurface coating is a paint.
 9. A method according to claim 3 whereinsaid surface coating is an adhesive.
 10. An article according to claim 2wherein said metal is aluminum.